It is well known that internal combustion engines wear at a faster rate during low temperature operation, such as that experienced upon initial operation of a cold engine. Considering the internal combustion engine of a motor vehicle, for example, upon initial operation of a cold engine the lubricating oil has drained into the crankcase and is highly viscous due to its flow temperature. Thus, the engine is operated for a time without adequate lubrication. Accordingly, it would be advantageous to more rapidly heat the reservoir of engine lubricant upon cold engine start-up. In addition, means have long been sought to increase the engine lubricant storage capacity both to reduce lubricant addition frequency and to extend the period between lubricant changes. Increasing the volume of lubricant stored in an engine lubricant reservoir, however, would exacerbate the above noted problem of inadequate engine lubrication during cold engine operation since, increasing the volume of lubricant would result in slower heating thereof.
Certain engine lubrication systems have been suggested, in which an auxiliary lubricant reservoir was employed to increase the total volume of stored lubricant. Such systems, however, have used lubricant from the auxiliary reservoir only to maintain the lubricant level in the primary lubricant reservoir. Thus, due to natural degredation of lubricant quality during operation of the engine, the lubricant in use is of a quality inferior to that of the unused lubricant stored in the auxiliary reservoir. An engine lubrication system exemplary of those adapted merely to maintain the level of lubricant in a primary reservoir is disclosed in Rath, Jr., U.S. Pat. No. 3,876,037 wherein a control circuit operates to open a conduit from a reserve tank to a primary tank. There is no teaching of recirculation of oil to the reserve tank. The engine lubrication system shown in Pellizzoni et al U.S. Pat. No. 3,712,420 employs a primary reservoir and an auxiliary reservoir with means for maintaining the proper oil level in the primary reservoir. Although the system provides for recirculation of lubricant through the auxiliary reservoir, there is no means provided for accelerated heating of the lubricant. The teaching in Liebel et al U.S. Pat. No. 3,335,736 also includes a device for controlling the addition of oil to an engine from a reservoir tank. Additional known systems employing auxiliary tanks to maintain a proper lubricant level in a primary tank are shown, for example, in Mettetal, Jr. U.S. Pat. No. 2,946,328 and Pitney U.S. Pat. No. 2,564,231. Tibeau U.S. Pat. No. 2,588,778 discloses a tank within a tank arrangement for maintaining lubricant level.
Previous attempts to provide means for heating engine lubricant include Miller U.S. Pat. No. 1,579,231 and Ringlund U.S. Pat. No. 1,269,310, each of which teaches the use of engine exhaust gas to heat lubricating oil directly in the oil pan of a motor vehicle engine. There is no suggestion of means for accelerated heating of a portion of the lubricant. Similarly, U.S. Pat. No. 1,989,585 suggests locating a heat exchanger within a motor vehicle crankcase, through which heat exchanger engine cooling liquid is circulated. The teaching of Ramsaur et al U.S. Pat. No. 1,902,970 is directed primarily to a particular design for a heat exchanger and suggests the use of two such heat exchangers, one for heating and one for cooling engine lubricant. Others have suggested lubrication systems comprising means for cooling the lubricant. Exemplary of such teachings are Donath U.S. Pat. No. 3,465,847 and Casting et al U.S. Pat. No. 4,324,213.
It is an object of the present invention to provide an engine lubrication system comprising an auxiliary lubricant reservoir wherein lubricant is recirculated between the primary lubricant reservoir and the auxilary reservoir. Notwithstanding the increased volume of recirculating lubricant, it is another object of the invention to provide preheating or accelerated heating of the lubricant delivered to the engine.